Castle Douglas is built next to Carlingwark Loch in which traces of prehistoric crannogs can be found, evidence of early inhabitation of the area.

The hoard of tools of iron and bronze is probably Romano-Belgic of the late first or early second centuries AD and is likely to have been a votive offering.

To the North of the town Glenlochar is the site of two successive Roman forts, the first being erected during the invasion of Agricola and the second during the Antonine period.

The development of a military road through Galloway built by Major William Caulfeild passed through the Carlingwark area and improved transportation connections in the 18th century.

It was acquired by Joseph Train, FSA Scot., the local antiquarian and author who presented it to Sir Walter Scott for his collection of antiquities at Abbotsford House.

A plaque records that in 1935 Henry J. Hewat of Paterson, New Jersey, USA, donated the present clock tower to the town.

Freeman Wills Croft set a key scene in his 1930 novel "Sir John Magill's Last Journey" at Castle Douglas Railway Station.

St John the Evangelist Catholic Church was built in 1867 by the London architect George Goldie and is Category B(S) listed building.

From March 1943 to April 1944, the town was the base for 92nd (Loyals) Light Anti-Aircraft Regiment, Royal Artillery, which was training for Operation Overlord, the invasion of occupied Europe.

Nissen huts were set up at Carlingwark Loch to house the troops while other billets included a church and a bowling clubhouse.

Also on King Street are Italian, Chinese and Indian restaurants as well as pubs and hotels serving meals and several take-aways.

There is a large car park at Market Hill at the top of the town next to the Heart of Galloway Visitor Centre.

[15] The town has a vibrant Community Centre on Cotton Street with over 600 users and is home to The Fullarton, a theatre opened 1996 in the building of the former St Andrew's Church.

2329 (Castle Douglas) Sqn[a] Air Training Corps is located in the town and are active within the local community, as well as offering young people between the ages of 12 and 20 opportunities to fly, visit RAF stations across the UK and experience adventures.

Castle Douglas Library[16] situated on the Market Hill, was designed by architect George Washington Browne and opened in 1904 with funding from Andrew Carnegie, the Scottish - American industrialist and philanthropist.

As with the remainder of the UK, Castle Douglas has a climate classified as Oceanic (Köppen: Cfb), resulting in moderate temperatures, year round rainfall, and windy, often cloudy conditions.

The nearest Met Office weather station is at Threave, about 1+1⁄2 miles (2.5 km) west of the town centre.